1. Field of the Invention
The present invention relates to control devices for controlling automatic engine stop and start. The control device is capable of automatically stopping the internal combustion engine of a vehicle on receiving an automatic engine stop request, and automatically restarting the internal combustion engine on receiving an engine restart request.
2. Description of the Related Art
There is a recent trend for vehicles to be equipped with an automatic engine control system capable of automatically stopping and starting the internal combustion engine of a vehicle in order to improve fuel consumption and reduce exhaust gas emission. Such an automatic engine control system is called the “engine idle stop control system”. The engine idle stop control system can automatically stop the engine when the driver intends to stop the vehicle, and automatically restart the engine when the driver of the vehicle performs various operation units in order to restart the engine, for example, the driver of the vehicle depresses the clutch pedal, releases the brake pedal, and operates the shift lever of the vehicle.
In general, the engine starter mounted to the internal combustion engine of a vehicle is comprised of an electric motor for pushing the pinion gear to a ring gear which is fixed to the internal combustion engine in order to engage the pinion gear with the ring gear. This makes it possible for the pinion gear to be cranked with the ring gear fixed to the rotary shaft of the internal combustion engine. However, when the rotation speed of the pinion gear is different from the rotation speed of the ring gear, that is, when there is no synchronization of rotation speed between these gears, there is a possibility of generating large gear meshing noise and damage between these gears because the pinion gear cannot be smoothly meshed with the ring gear due to such a large difference of rotation speed between these gears.
Conventional patent documents, for example, Japanese patent laid open publication No. JP 2002-122059 has disclosed a conventional technique which restarts the internal combustion engine of a vehicle by the following steps (a1) and (a2) when an engine restart request is generated while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, in particular, immediately when the internal combustion engine is automatically stopped caused by the generation of an automatic engine stop request:    (a1) The pinion gear is meshed with the ring gear which is fixed to the crank shaft of the internal combustion engine after the rotation speed of the internal combustion engine (or the rotation speed of the ring gear) is almost zero before completely stops; and    (a2) After the step (a1), the starter motor rotates the pinion gear in order to start the cranking.
The above engine restart control will be referred to as “pre-gear meshing control”.
However, because the pre-gear meshing control starts the cranking after the rotation speed of the internal combustion engine is almost stopped when the engine restart request is issued while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, a delay time period counted from the time when such the engine restart request is issued to the time when the internal combustion engine is actually restarted. This delay time period gives uncomfortable drive to the driver of the vehicle.
In order to solve the above conventional drawback, there are other conventional techniques disclosed in Japanese patent laid open publications No. JP 2005-330813 and JP 2002-70699, which restart the internal combustion engine of a vehicle by the following steps (b1) and (b2) when the engine restart request is issued while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop by the automatic engine stop request:    (b1) The pinion gear is meshed with the ring gear which is fixed to the crank shaft of the internal combustion engine after the rotation speed of the pinion gear is synchronized with the rotation speed of the ring gear so as to decrease a difference in rotation speed between these gears; and    (b2) After the step (b1), the starter motor drives the pinion gear to start to rotate in order to perform the cranking.
The above engine restart control will be referred to as “pre-gear synchronizing control”.
When the rotation speed of the internal combustion engine is relatively high when the engine restart request is issued while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, it is possible for the control device to restart the internal combustion engine without performing the cranking by the starter. The above engine restart control will be referred to as the “engine self-restart control”.
When the engine restart request is issued while the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, the conventional technique disclosed in JP 2002-70699 executes:
(X1) the engine self-restart control when the rotation speed of the internal combustion engine has a value within a first rotation speed range which is higher than a first rotation speed;
(X2) the pre-gear synchronizing control when the rotation speed of the internal combustion engine is not more than the first rotation speed and within a second rotation speed range which is higher than a second rotation speed; and
(X3) the pre-gear-meshing control when the rotation speed of the internal combustion engine is within a third rotation speed range which is not more than the second rotation speed.
However, there is a possibility for the control device to cause a failure of the engine restart even if performing the engine self-restart control. For example, there is a high possibility for the control device to cause a failure of the engine restart when the dropping rate of the rotation speed of the internal combustion engine is high. In the conventional control method disclosed in JP 2002-70699, the pre-gear synchronizing control is executed when the rotation speed of the internal combustion engine is decreased within the second rotation speed range after the engine self-restart control causes a failure of the engine restart.
However, as shown in FIG. 6, the rotation speed of the internal combustion engine oscillates forwardly and backwardly after the automatic engine stop. That is, the rotation speed of the internal combustion engine is greatly decreased at the time of the engine compression stroke, and the rotation speed of the internal combustion engine is slightly increased during a period other than the engine compression stroke.
Accordingly, there is a possibility that the rotation speed of the internal combustion engine becomes a value which is higher than the second rotation speed range when the control device performs the pre-gear synchronizing control at the time t20 when the rotation speed of the internal combustion engine is decreased within the second rotation speed range after the time t10 when the control device fails in engine self-restart control.
In this case, because the pinion gear is pushed to the ring gear side while the rotation speed of the ring gear is greatly larger than that of the pinion gear (that is, under the condition where the rotation speed of the ring gear is not synchronized with that of the pinion gear), it becomes difficult to smoothly perform the gear meshing operation between the pinion gear and the ring gear. This generates large gear meshing noise and abrasion of the ring gear and the pinion gear, and causes large impact to the starter.
When the control device fails in performing one of the engine self-restart control, the pre-gear synchronizing control, and the pre-gear meshing control, there is a possibility that the rotation speed of the internal combustion engine becomes a value within the rotation speed range which corresponds to the above control which causes the engine restart failure. In this case, the control device executes the same control again, and this has a high probability of causing the same engine restart failure.
By the way, there is a possibility of causing the engine restart failure due to an engine trouble such as a difficulty of performing the desired engine combustion even if the control device executes the engine self-restart control. Further, there is a possibility of causing the gear meshing failure by pushing the pinion gear to the ring gear when no gear synchronization of rotation speed between the pinion gear and the ring gear is obtained even if the control device executes the pre-gear synchronizing control.
Further, there is a possibility of causing the engine restart failure on the basis of the gear meshing failure due to aging deterioration of the pinion gear or the ring gear.
Still further, there is a possibility of causing the gear meshing failure due to aging deterioration even if the control device executes the pre-gear meshing control.
For example, the conventional technique disclosed in JP 2002-70699 executes the pre-gear synchronizing control when the rotation speed of the internal combustion engine is decreased within the second rotation speed range due to the engine restart failure caused by the engine self-restart control. However, it is generally difficult to estimate the motion of the rotation speed of the internal combustion engine immediately after the engine restart failure occurs. Further, because the starter motor rotates by momentum, it is difficult for the control device to detect the rotation speed of the starter motor with high accuracy. Accordingly, while the rotation speed of the internal combustion engine is dropping due to the failure of the engine restart control, it is extremely difficult for the control device to detect the gear synchronizing time and execute the pre-gear synchronizing control drive at the gear synchronizing time in order to drive the electromagnetic actuator to mesh the pinion gear with the ring gear. This causes damage to and causes deterioration of the ring gear and the pinion gear because the control device and the electromagnetic actuator cannot smoothly mesh the pinion gear with the ring gear.
Still further, in the case where the control device executes the pre-gear meshing control when the rotation speed of the internal combustion engine is decreased within the third rotation speed range after the engine restart failure caused by the pre-gear synchronizing control, there is a possibility for the control device to drive the electromagnetic actuator to push the pinion gear to the ring gear when the rotation speed of the internal combustion engine is within the second rotation speed range because it is difficult to estimating the rotation speed of the internal combustion engine immediately after the engine restart failure. This also causes damage to and causes deterioration of the ring gear and the pinion gear because the control device and the electromagnetic actuator cannot smoothly mesh the pinion gear with the ring gear.
Still further, in the case where the control device executes the engine self-restart control again when the rotation speed of the internal combustion engine is within the first rotation speed range after the engine restart failure caused by the engine self-restart control, there is a possibility for the control device to executes the engine self-restart control when the rotation speed of the internal combustion engine is within the second rotation speed range because it is difficult to estimate the rotation speed of the internal combustion engine immediately after the engine restart failure. This would cause the engine restart failure again.